This posting is older than 6 months and can contain outdated information.
When the keyboard is active, the left, right, up, down and play
buttons are needed for controlling the virtual keyboard. Your mapping
for these buttons is overridden as long as the keyboard is active.
You can dismiss it with the Menu button.
Also, if you use a remote with more buttons than the Apple Remote, you
can set show and hide actions to other buttons than left, right, up,
down, play and they'll work just fine.
Best regards,
Felix Schwarz